The vast majority of tubular support posts such as sign posts used along streets, roads and motorways are steel tubes. The steel posts are used in various sizes depending on the sign load and application conditions. Typically steel posts are available in standardized sizes and shapes and hence the installation aids to be used with these standard sizes are standardized as well. Steel posts withstand weathering for up to 15 years before they require replacement.
One problem with steel sign posts is that during a vehicle collision, the steel post will generally not give way upon impact. Because the post remains rigid close to ground level, it can penetrate the vehicle. In many cases, the vehicle is already out of control when it hits the post, so can hit it at any angle. This type of impact can result in fatalities and serious injuries to the vehicle occupants, particularly if the impact is side-on. Hence, there exists a desire to find alternative posts that have less potential for causing vehicle damage and less potential for injury. National governments and authorities are continuously attempting to enhance the road safety and increase safety of the road infrastructure. In particular, some authorities have developed passive safety requirements for sign posts used on the side of streets. An example thereof is European Standard EN12767 which classifies sign posts in categories depending on energy on impact at a particular vehicle speed. EN 12767 specifies requirements for passive safety and defines levels in passive safety terms intended to reduce the severity of injury to occupants of vehicles in impact with roadside structures. The levels of passive safety in this standard are defined in terms of High Energy (HE), Low Energy (LE) and Non-Energy (NE), which are determined by measuring the speed of the vehicle at a point beyond impact and comparing with the defined impact speed. The difference in these speeds relates to the energy of impact. Energy absorbing support structures may slow the vehicle considerably and thus the risk of secondary accidents with structures, trees, pedestrians and other road users can be reduced. Non-energy absorbing support structures may provide a lower primary risk of injury caused by the initial impact with the said support structure than energy absorbing support structures. Occupant risk levels are also defined on a scale of 1 to 4, in order of increasing safety. Levels 1-3 for a particular speed class require a test at 35 km/hr and at one of 50, 70 or 100 km/hr and level 4 requires only to be tested at the class speed.
It would now be desirable to develop a tubular support and in particular as a sign post in traffic and which tubular support meets various national standards for passive safety. For example, it should have a non-energy (NE) or a low energy (LE) classification under EN12767 at a speed of impact of 50, 70 or 100 km/hr. An element in achieving this classification is the energy absorbed by the support, when impacted, which should be minimized, i.e. the support should be designed to give way upon impact. Of course it would be desirable to develop such a tubular support in such a way that other performance requirements typically imposed on sign posts can be met as well. In particular, the support is desired to have appropriate stiffness and strength to hold a sign under the expected design loadings resulting from wind pressure on the sign and wind buffeting. It would be desirable to develop posts meeting the requirements of EN12899 and corresponding standards in other countries. It is interesting to note here that typically the desire to have NE or LE classification under EN12767 and the strength and stiffness requirements under EN12899 are competing properties.
For example, in U.S. Pat. No. 4,939,037 there is described a composite sign post for replacing the steel post. The sign post disclosed therein comprises longitudinal and/or transverse arranged fibers in a resin matrix. Typically used and disclosed fibers are glass fibers. However, the problem with a composite sign post based on glass fibers as disclosed in this US patent is that the stiffness performance of such a post will be at the lower end of what is required. While this could be solved by increasing the wall thickness of the post, this would also imply that the passive safety features are reduced, hence illustrating the competition between strength and passive safety. Alternatively, it could be contemplated to increase the diameter of the post but this would likely mean that the size would fall outside the standardized ranges of steel posts with the consequence that installation equipment adapted for use with steel posts cannot be used. Additionally, the size of such a post might contribute to road hazards by unduly obstructing the view of road users, and become aesthetically displeasing. This would likely lead to its rejection by highways authorities.